Whale Poo

It turns out that Whale Poo# is vital to the ecology of the oceans.  Or at least it was when we had plenty of whales.  The lack thereof may explain part of the decline of our world fisheries.  I am not arguing against the devastating effect of our overfishing.  I'm not arguing against the destructiveness of our fishing methods.  They too are clearly trashing our fish resources but, with lots of whales, the amount of fish we could take sustainably would increase.

#Also see New Scientist, 9 July 2011,p36


It turns out that whales pump nutrients from deep water and urinate and defecate them into surface waters.  Even better, whale defecation is floculant and tends to float in surface waters where it powers the surface ecology.  You probably immediately thought of Sperm Whales who eat giant squid from great depths but some of the baleen whales also pump nutrients.  For instance Gray Whales skim the sea bottom collecting bottom organisms and mud.  They filter out the mud through their coarse baleen.  Humpbacks herd shoals of fish and Krill to the surface where they can trap them against the surface to feed on them.  It has been found that Krill, in contrast to what was once thought, often are also found at great depths feeding on the bottom.  Undoubtedly, as we learn more about these animals we will find more about how they bring nutrients to the photic zone.


Moreover, whales are part of the trapping of nutrients in surface layers.  Let me digress for a moment.


There is often confusion between the observed biomass and the biodiversity of an environment on the one hand and the amount of  sustainable harvesting which is possible on the other.  The first people who looked at tropical forests and tropical coral reefs saw a huge biomass of animals and an astonishing diversity of animals and plants. It was fairly natural to assume that one could harvest huge quantities of food and other valuable resources from both.  Unfortunately, the large biomass relates more to the ability of these environments to hold and recycle nutrients within their ecological system.  The incredible diversity of species is partially related to how long they have been stable ecological regimes with huge spans of time for diversity to occur.    In the Amazon jungles, for instance, the huge area covered by jungle obtains its nutrients from the weathering of the Andes mountains to the West and from dust blown from the Sahara desert.  When parts of the jungle are cleared and farmed, it has been found that after a couple of crops, the soil is exhausted.  Similarly, coral reefs when heavily fished are soon exhausted.  Coral reefs exist in very nutrient poor water.  In fact, they can only live in very clear and hence nutrient poor water.    Coral polyps contain zoozanthellae, a type of algae, and they need sunshine to live.  Corals polyps have evolved to grow in very poor waters by evolving a symbiotic relationship with internally contained algae and  now can not grow in rich, algae filled water as their symbiotic algae will not get enough light.  Not a lot of nutrient enters the coral environments and so not much food can be sustainably removed.


Compare this with any of the upwelling environments off desert coasts such as the coast of Peru or the coast of South West Africa.  There, nutrient rich water wells up from below and the productivity and harvestability is astounding.  Much of the fish meal for the world, for instance, comes from the anchovy off the coast of Peru.  The species diversity is nowhere as great as on a coral reef or in a jungle but the productivity and hence the amount that can be sustainably harvested is huge. 


So back to the whales.  There are two factors that lead to huge biomass in an environment.  As we have seen one is the influx of nutrients and the second is the ability to hold these nutrients in the system.  If you only had phytoplankton and krill in a region, the krill would  eat the phytoplankton and new phytoplankton would grow at a rate that depended on the amount of nutrient coming from outside of the environment.  Feces and dead krill would sink to the bottom of the ocean and nutrients would be lost from the surface.

The ultimate limiting factor in the growth of algae is the amount of sunshine falling on the water.  With an unlimited supply of nutrients in the water, the maximum amount of  sun energy can be used.  However, as nutrients are depleted, the total productivity is limited by the nutrients left in the system**.  In oligotrophic environments, productivity is very low despite the amount of sunshine falling on the water.  Whales, feeding on the surface, are  continually  mineralizing* the krill and excreting nutrients in a form that can be taken up by the algae.  More sun energy is being used and nutrients are being fixed into whale biomass.  Krill grow at a huge rate, fed by the huge primary productivity.  Nutrients entering the system are captured and kept at the surface.    This is a very simplistic painting of the picture.  There are many many other parts to the web of life that capture and use feces from all the surface organisms and mineralize them and all of them conspire to keep nutrients in the photic zone.  Add to this the  upwelling and the nutrient pumping due to the whales and productivity can be truly astounding.  So, whales not only pump nutrients from below the photic zone but contribute to keeping the nutrients within the photic zone.

*Mineralization:  The break down of proteins, sugars, starches etc into a form in which algae can utilize them.
** The law of the minumum which states that the growth rate of an organism (or a system) is proportional to the input which is smallest in comparison with the amount just needed for unlimited growth.

The law of the Minimum Resource

Widening out our horizon a little, the same idea holds true in the ocean when looking at the productivity of an area.  Water is no problem as growth is in water.  Nutrients can be present in larger or smaller quantities depending on upwelling, biological activity and so forth.  The ultimate limit over which we have not control is sunshine.  It powers the bottom layer of productivity, the phytoplankton, and determines the maximum productivity that can occur.  When looking at a fisheries such as the Anchovy off Peru, it is interesting to note that anchovy are at the third trophic level.  They eat zooplankton that in turn eats phytoplankton.  The total productivity of Anchovy is therefore only about 1% of the productivity of phytoplankton#.

#as a rule of thumb, 10% of the biomass of any trophic level is passed on to the next level.  100kg of phytoplankton makes 10kg of zooplankton which makes 1kg of penguin which makes 0.1kg of sea lion.

The bottom line is that with their dual function of bringing nutrients from below the photic zone and of keeping the nutrients at the surface, whales greatly enrich the environment for the growth of other organisms, some of which are commercially exploitable fish. 

Another aspect of the story involves where whales go to give birth.  This is generally in tropical waters such as around our Pacific Islands or in the Gulf of California.  The adult whales for the most part do not feed there but they nurse their young and the young poop nutrients out into the water.  By killing whales we are robbing people in these tropical waters of their source of food.

To anyone that doesn't buy the argument that we should not kill whales because they are such magnificent animals or because they are good for tourism, perhaps this is a more hard nosed argument for leaving them alone.  Whales increase the productivity of fish.



 

Continental Glacier Meltdown

Over the past 2.5m year ice age numerous glaciated periods (glacials) and warm periods (interglacials) have come and gone.  The most recent continental glaciers began to melt around 20,000 years ago and really got underway away about 11,000 years ago leaving ice sheets only in Antarctica and Greenland.  The end of glacials appears to be synchronous with one of the Milankovitch cycles; namely the variation in the tilt (obliquity) of the earth's axis.  At the beginning of the present  ice age, which we are in the middle of, the cycle was 41,000 years.  However over the past million years of the present 2.5 million year Glacial Age, only every third or so obliquity nudge has resulted in an interglacial.  Glacials over the past million years or so have been lasting on the order of 100,000 years.  Coincidentally with the melting of continental glaciers there is a sharp rise in Carbon dioxide  

<sub>As suggested in a previous blog it seems unlikely that some sudden source of Carbon dioxide would occur exactly in sinc with the Milankovitch cycle.  As odd as it seems it is more likely that the rise in CO2 is somehow the result of the melting.  Of course, once sufficient CO2 is released, a run-away melting will occur.  One likely positive feed back (warming causing more warming) is the ability of the oceans to hold less Carbon dioxide when they are warm than when they are cold.  As warming starts, presumably as a result of obliquity, the oceans could give out Carbon dioxide or at the very least, not absorb as much.

In a previous blog, I suggested that methane clathrates and carbon dioxide clathrates could accumulate under an ice sheet once it had thickened to a few hundred meters.  Sources of methane and Carbon dioxide include coal measures, liquid and gaseous hydrocarbon deposits and shale beds as well as the decomposition of organic material buried by the accumulating ice.  If the ice covered over an area of permafrost**, the methane stored in the permafrost could also find its way to the bottom of the ice sheet.   Ice sheets cause the depression of the land by about a third of a km for every km of ice added^# and this might well act as a natural 'fracting', increasing the escape of such gases from all the mentioned sources.  All this carbon would be sitting there  at the bottom of the ice sheet ready to be released if the continental ice sheet started to melt.  If sufficient was released in a burst, the green house effect could lead to a feedback, melting more ice causing the release of more gas and causing more melting etc.  This run-away greenhouse effects would only end when the ice sheet was all melted.  Following the melt, the slow ever present sequestering of carbon in the various carbon sinks would continue until it was possible for the accumulation of snow to start again.

# The basaltic rock on which the continents float has a specific Gravity (SG) of just over 3. Hence a km of ice with a specific gravity of  a tad under 1 would push down the continent about a third of a km.

**It is interesting to note that if snow is accumulating on an area of permafrost, the snow will insulate the underlying ground.  The 0 degree contour at the bottom of the permafrost will move upward as geothermal heat melts it.  Eventually, as the ice sheet deepens, all the permafrost, often rich in organic soil and methane clathrate, will be melted.  The permafrost undergoing anaerobic break down and any already stored up methane* would be available to combine with the bottom layer of ice and form methane clathrate.

 
In this blog, I would like to suggest  mechanisms which would explain why every nudge from the Milankovitch cycle does not end an ice age.  Lets do a mind exercise.  

Consider for simplicity a large continent like Australia.  It is shaped like a hockey puck, flat on top with very little slope in any direction.  Enough carbon has left the atmosphere and become sequestered in sinks for some snow to  last through the summer.    The process of going into a glacial is gradual.   The accumulation of snow can only proceed at the rate of precipitation in the area of accumulation minus sublimation and melting.  The process is somewhat accelerated by the albedo effect.  When a significant area is covered with white snow, incident light is mostly reflected back into space increasing the  cooling.

Snow occupies about 10 times as much volume as an equivalent weight of water but as the snow deepens, the weight of overlying snow on the bottom layers increases and air is squeezed out.  By the time there is a hundred or so meters of snow, the bottom layers have been squeezed into ice with some inclusions of air.  The ice at the bottom occupies about 10% more volume than an equivalent weight of water.


When the ice is only a few hundred meters thick it just sits there getting deeper and deeper.  The land is flat so it doesn't move down hill and there isn't enough pressure yet to squeeze ice outward.  At about 300m depth, there is enough pressure at the bottom of the ice layer for clathrates to form.  Any methane or Carbon dioxide which is coming from the underlying land combines with the ice and is trapped.

When the ice has reached a km or so in depth, the pressure is great enough that ice begins to be squeezed toward the edges.  Right in the middle of our hockey puck continent, there is no motion with respect to the underlying land.  As you go toward the edges, the motion is faster and faster.  Fast is all relative.  Even in glaciated continents such as Greenland with 3 or so km of ice at the center, the motion at the edges is only a few to a few tens of meters per year.  There are some individual glaciers which carry ice from the interior which are moving as much as 12km per year but this is down specific valleys and not along the entire perimeter of the glacier.   Averaged over the years, ice can only fall off the edges at the rate that it accumulates on top.   Since continental glaciers reach depths of at least 3km,  clearly, less ice was expelled than has was accumulated over the formation of the 3km deep ice sheet.   At some point, as the ice thickens, the rate of loss of ice will equal the rate of accumulation.  It is likely that toward the middle of the continent, the ice doesn't move at the bottom relative to the land but is rather squeezed out of the middle layers of the ice.  Toward the edges, ice would be moving over the ground.


Each Milankovitch nudge will probably result in some melting.  If it is correct that clathrates have been collecting at the bottom of the ice sheet, this will cause an increase in the output of green house gases  and the thicker the ice the faster this might occur due to faster rate of spread caused by the thicker ice. Also, the faster the ice is moving, the further into a melting climate the ice will be pushed.   This may be the explanation for the start of an interglacial only every few Milankovitch nudges.  Presumably a certain amount of green house gas is necessary to initiate a run away melting.  The older an ice sheet, the more clathrate could accumulate at the bottom and the thicker the ice sheet, the faster its borders are moving outward. Therefore, the older and thicker an ice sheet and the more clathrate it has accumulated, the greater the chance of a run away melting when an obliquity nudge occurs.

As a further factor, with a thick ice sheet, the glacier at the edge will be moving across the ground and expelling clathrate.  It would be expected that the concentration of clathrate would increase as you go toward the centre of an ice sheet.  As the ice sheet edge melts back, more and more clathrate breaks down into the atmosphere.  The thicker the ice, the more clathrate is likely to be stored under the ice and the faster the ice is moving at the edges.  Thick ice should be much less stable than thin ice.

Another factor which might be relevant is the heat coming out of the earth.  Although it varies widely from location to location, the temperature increases as you go down into the earth at about 25 degrees C per km.  Put a layer of ice on the ground and this heat has to work it's way up to the surface of the ice.  I haven't been able to find the factor for heat transmission in rock and in ice  in  order to compare them but for the sake of the argument let's say it is the same.  Let's also assume that the average temperature at the top of the ice sheet is -50C.  If the ice is 1km thick, the temperature at the bottom of the ice would then be -25degrees.  If the ice is 2km thick it would be 0 degrees.  If three km thick, +25 degrees.  Of course in this latter case this wouldn't be so.  The heat comes in contact with ice which melts at 0 degrees and absorbs a lot of heat doing so (latent heat of fusion).  Have a look at this link (maps half way down in the PDF file) which show calculations for the basal temperature of the Antarctic Ice sheet.

The result is that with over 2km of ice depth and given some time to reach equilibrium, there should be water at the bottom of the ice sheet.  Here we run into another wee codicil.  If, as was suggested in a previous blog,  methane clathrate has accumulated at the bottom of the ice sheet, it can stay frozen up to 18 degrees centigrade with sufficient pressure.  Whatever the actual case, the general principle is that with a sufficiently deep ice sheet, the bottom layer should be melting.  This may be another part of the explanation as to why only every three or so nudges by the Milankovitch cycle sets off an interglacial period.  A sufficient depth of ice has to first collect to cause heat from the earth to liquefy its bottom and increase its horizontal movement on this lubricating layer .  So what sort of evidence would support this hypothesis.


Test

     A) at the bottom of present ice sheets, the temperature should be around 0 degrees.
     B)  There should be lakes below deep ice sheets where the topography allows.
     C)  It should be possible in some locations at least, to detect methane and possibly Carbon dioxide being evolved from the edges of  ice sheets where they are melting.
     D) Where ice sheets exit into the ocean and are at least 30m above sea level (and hence their base is 300m below sea level) there may be clathrates on the bottom layers in some locations.
     E) Since the carbon released from the bottom of a 100,000 year ice sheet would be "old carbon" (in other words, carbon depleted in C14) There should be a dating anomaly from the end of the last ice period, 11,000 years ago*.  This sudden influx of old carbon into the atmosphere should make wood, growing after the melting, look older.  For wood from about 11,000 years ago, one might see successive growth rings from a tree looking older and older despite the fact that they each successive growth ring is younger than the previous one.  A place to find suitable wood might be in tropical swamps where a log had sunk into the anaerobic mud or high mountains where trees such as the Bristle Cone Pine exist.
    F) if the bottom layer of an ice sheet is composed of clathrates, you might find that even though a core found solid ice right to the bottom of the core, the temperature could be above 0 degrees.  Clathrates can exist up to 18 degrees centigrade with sufficient pressure.  In fact, you might find a liquid layer at the bottom of the ice with a clathrate layer below the liquid layer. 

Of course, if the bottom of the glacier is moving horizontally at locations where there is permafrost, it will be scraping off the permafrost layer and carrying it toward the edge of the ice sheet with it's entrained load of clathrates.  If the ice sheet is frozen to the base and is only moving laterally due to the middle being squeezed out, the clathrates will only be released when that part of the glacier melts. 

A last contributor to sudden melt down and release of Carbon dioxide is Moulins. Moulins are  vertical shafts which are caused by melt water pouring down fissures in continental glaciers.  At present this phenomenon is best observed on the Greenland ice sheet where there is increased melting each summer.  Pools of water form on the surface of the ice and if they find a fissure, they pour down to the bottom of the ice sheet.  This water has to come out somewhere and presumably it will find its way out at the edges of the ice sheet.  It would be expected that it would carry with it the material from the bottom of the ice sheet.  Part of this would be the clathrates that have accumulated there.  At each Milankovitch nudge there would be expected to be surface melting and a wash out of some of the bottom material.  If great enough, this would result in a run away green house effect. It should be possible to detect methane where streams come out under continental ice sheets.


All the above scenarios depend on the supposition that clathrates will accumulate under continental glaciers ready to be released when the glacier melts.  The longer the glacier exists, the greater the accumulation should be.   If this is indeed happening, it should be observable under our two remaining continental glaciers on Antartica and Greenland and even possibly Iceland.

*At a pinch, carbon dating can go back 50,000 years.  Hence it would be perfectly useful for dating objects from the end of the last glacial but wouldn't extend back to the previous interglacial which was 125,000 years ago.

In summary
The older and thicker an ice sheet, the more unstable it should be.  This may  be due to:
1) Higher temperatures at the bottom of thicker ice sheets than more shallow ice sheets due to geothermal heat being insulated from escape due to the insulating properties of the ice.  At a sufficient thickness a layer of water at the bottom of the ice sheet would accelerate its flow outward.
2)  A greater accumulation of carbon in the form of clathrates the longer a glacial lasts and hence the larger available green house effect if the ice sheet starts to melt.
3) A greater speed of spread at the edges of an ice sheet, the deeper the ice is, pushing ice into geographical areas where it will melt.  If this ice has got a bottom layer of clathrate, this will be entering the environment.  Above some critical amount of carbon added to the atmosphere, a run away green house effect would occur. A nudge by the Milankovitch cycle would release more methane from a thick ice sheet than a shallower one.
4) Outwash of bottom material by surface melt and Moulins at each Milankovitch nudge.  The longer the ice sheet exists, the more carbon there should be available to be washed out.

Note that methane is often quoted to be 20 to 30 times as effective a greenhouse gas as carbon dioxide.  This only holds on a 100 year basis.  Methane oxidizes in the atmosphere to Carbon dioxide with a half life of about 8 years.  If we look at the effect of, say, a cubic meter of methane over 100 years and calculate how much warming it will cause, it will cause 20 to30 times as much warming as a similar amount of CO2.  However, the actual strength of methane as a greenhouse gas is more like a hundred times as much as Carbon dioxide.  This is only important if methane is being introduced into the atmosphere in very large quantities (as seems to be the case now).


PS (Dec24, 2012)
A recent paper by German authors has shown that volcanic activity increases following strong ice melt.  This would also go some way to explaining the increase in carbon dioxide in the atmosphere following, rather than before ice melt.</sub>

 

By by Coral Atolls

There is much to-do in the press about the immanent drowning of coral atoll islands due to rising sea level.  While climate change could well destroy coral atolls, it  won't be primarily due to the rise in sea level.  Some background:

The present ice age, which we are in the middle of,  started roughly 2.5million years ago.  It has had numerous glaciated periods (glacials) and warm periods (interglacials).   The  interglacial before the one we are in now, we call the Eemian.    It was centered about 125,000 years ago.  That is 62 times as long as from now back to the Roman empire.  The present interglacial we are living in we call the Holocene.  As the previous (Eemian) interglacial, faded away sea level fell as more and more water was deposited as snow on the continental glaciers*.  At its greatest extent, sea level was 120m below its present level.  Of course the corals that were growing within 120 meters of the surface of the ocean during the Eemian interglacial, were killed as sea level dropped.  Without live corals to resist the effect of waves, these islands would have eroded.  They may well have eroded down to the level of the  low tide mark, 120 meters below present low tide.   A lot of erosion can occur in more than 100,000 years.

 

*In the western hemisphere, glaciers start to accumulate on the high lands of Baffin Island and spread out from there.  

 
As the ice started to melt, some 20,000 years ago and really got under way 15000 years ago, sea level rose quickly as the continental glaciers flowed into the oceans.  The main melt ended 7000 years ago with a slow rise since then of about one mm per year.  Today, coral reefs all over the world are at about the current low tide level and Atoll islands are a few meters above high tide.  Clearly, corals have grown as the ice melted and sea level rose.  The corals have filled in the 120 or so meters between the low tide level at the maximum extent of the recent 'glacial' to the present low tide level*. The lesson is, as sea level rises, the restraint on coral growth is removed and they grow up to the current low tide mark.  The average sea level rise was about 14mm per year during the rapid melt with isolated periods of as much as 56mm per year. (today sea level is rising at about 3.5mm per year)

* Incidentally, the Calcium carbonate of which coral skeletons are made are a tad over 60% Carbon dioxide!!which ultimately comes from the atmosphere. This, under natural (without humans) conditions would be contributing to sliding us into the next glaciation as Carbon dioxide was built into coral.

OK,,,,,, so if corals are limited by low tide, why are the coral atoll islands meters above the level of the growing corals.  This question pertains to the present fear that coral islands will be swamped as the sea rises.

The answer, to a large extent,  is Parrot fish.  Parrot fish eat corals and digest the polyps.  They poop out coral sand.  A parrot fish typically produces 90kg of sand per year.  A thousand parrot fish in a lagoon and you have a production of 90 tons of sand per year.  The sand is moved by wind, currents and waves, especially during hurricanes,  and collects where the total energy is low*.  As long as the seas are healthy for corals, new ones grow providing more food for Parrot fish and hence more sand.

 Now we come to the function of hurricanes.  In a hurricane waves are longer and higher*. so they pick up, not only coral sand but coral rubble and deposit it where the energy of wind, currents and waves is low.  It is a sort of  one way valve.  This keeps the atolls supplied with sand and rubble which keeps them growing upward.  As long as nothing kills the corals (or the Parrot fish) coral islands will keep up with sea level rise.

*For those of you with a mathematic bent, for every ninth of a wave length  you go down in the ocean, the circle of rotation of a wave halves.  For instance, if you have a wave length of 18m and a height of 1m, if you go down 4m, the circle of rotation will be 25cm.  A long wave has an effect much deeper than a short wave.
 
Once the sand forms a bit of land above sea level, bird transported seeds can germinate and the resulting plants will dampen the force of the wind crossing the island.  This results in an increased catch of wind-blown sand on the island and a root system to retain what sand there is.  Once there is a bit of an island above the high tide, rain will accumulate in the soil of the island, floating as a lens above the sea water.  Varieties of plants, which need fresh water can then grow. Bird poop (Guano) will add to the fertility of the soil created.


So under natural conditions, it is unlikely that sea level rise will destroy the Atolls.  In fact some satellite pictures show them growing.  The real problem that climate change will cause is primarily due the increase in Carbon dioxide.  Two effects are at play here.  As the sea becomes more acidic due to the absorption of CO2, it becomes harder and harder for Calcium carbonate depositing animals to extract the calcium from sea water.  A bit more acidic, and  shells and corals will start to dissolve.  

The second problem which could come from climate change is temperature rise*.  The lethal temperature for corals is only just above the temperature of maximum growth which is, in turn, only a few degrees above the present water temperature.  There are a number of reasons that tropical seas could warm.  A major one is the shut down of the ocean circulation which is powered by two phenomenon.  The first is  freezing of Arctic (and Antarctic) water.  Fresh ice crystallizes out of the sea water leaving the salt behind.  This forms brine which sinks down to the bottom of the Arctic ocean and flows out of the Arctic.  This out-flowing deep water causes surface water to be sucked toward the poles, bringing with it calories.  Heat is being pulled from warmer regions of the earth, toward the poles.  Stop the formation of deep salty ocean water and no longer will this flow of heat exist and tropical areas will warm.

The second effect that powers the Gulf stream is the cooling of the somewhat saltier water that flows up the East coast of North America.  It only stays on top because it is warmer than the underlying water.  As it flows north into cooler climes, it cools as it gives up it's heat to the atmosphere until it is dense enough to sink down through the colder water below.  If there is an outflow of fresh water from melting continental glaciers, the mix of the surface, salty water with the fresh water from the ice will no longer sink as it cools.  Once again you get a reduction of the formation of deep oceanic water, and hence the reduction of surface water being pulled northward and the heat remains in tropical waters.

If the arctic overturn is stopped by increased melting of Greenland ice sheets, and by a reduction in the formation of oceanic ice,  we will have very cold winters in Europe despite the general warming of the planet.  The corollary is that heat will not be removed from southern waters.  If either acidification or temperature rise occurs, there is nothing that the people of the coral atolls can do**.  Without live corals and parrot fish to provide a constant source of coral sand, the islands will erode.   

** (Added Jan 2017)Note that in 2016, toward the end of a very severe El Nino there was wide spread coral bleaching.  Overall, each bleaching event seems to be more severe than the previous one.


Jason Buchheim reports 
As reef building corals live near their upper thermal tolerance limits, small increases in sea temperature (.5 –1.5 degrees C) over several weeks or large increases (3-4 degrees C) over a few days will lead to coral dysfunction and death. Anomalously high sea temperatures have often been reported in the Caribbean-wide series of bleaching events that occurred during 1986-88, leading to hypothesis that global warming was having an effect on the coral reefs in this region.

*If climate change results in an ice free Arctic ocean, it becomes a massive solar panel and could rapidly melt the Greenland Ice Sheet.  If fresh water pours into the sea sufficiently fast, this could shut down the ocean circulation system.  This system, as it warms northern Europe, cools the tropics.  Stop this cooling and tropical waters could reach a lethal level for corals.


However, Short of global acidification or a rise in the temperature  of the tropical oceans, the health of the coral atolls is in the hands of the local people. 

The three basic principles to avoid your atoll being swamped by the sea are: 

 
A) do nothing that damages corals, 
B) never kill a parrot fish and 
C) make sure the islands are vegetated so that any wind born sand across the island will land on the island for the root system to hold there.  

More specifically:

*  Don't use fishing methods that damage coral reefs.  This includes dynamite.
*  Don't use chemical fertilizers on land.  They can damage corals when they seep into the sea.  If land sourced nutrients are sufficient they can lead to phytoplankton blooms that shade the zoozanthellae that are necessary for coral health.They can also fertilize sea weed growth which can smother reefs.
*  Don't allow sewage to flow into the sea or into the water table unless it is fully treated.  Primary or even secondary treatment is not sufficient.  The nutrients must be removed.
*  Don't use pesticides or herbicides as they can harm sea organisms.
*  Don't over utilize the fresh ground water.  The vegetative cover of the island 
depends on this fresh water
*  Never ever ever harm a parrot fish
*  Leave the rabbit fish (Siganid sp.) alone too.   They eat algae that can smother corals. (third fish down in the link)
*  Reintroduce the system of Tapu (taboo) in which large sections of the reef are off limits to utilization of any kind for a number of years.  Every decade or so the area is changed.  Fishing in  areas not under Tapu will be greatly improved as a bonus because of the recruitment of fish from the tapu area.

Short of a global situation that kills the corals, the fate of the atolls is in the hands of the local people.   The elephant in the room, of course is population control.  All the strains on coral atolls mentioned above are exacerbated by over-population.  Atolls are microcosms of the situation the whole world is in at present.  With stable or decreasing numbers of people on coral islands, all the bad effects decrease to manageable proportions.

By the by, an interesting experiment to try would be to plant some mangroves in shallow water by the land. If they grow, they will catch sand from the water currents which will further increase the available real estate and will protect the land during hurricanes.  Mangrove  areas are also apparently great breeding grounds for fish. They are also areas of low energy where sand will accumulate during hurricanes.  Just a thought.

Final conclusion 
The future existence of coral atolls depends on the health of the corals and the presence of fish which turn corals into sand.  The corals respond by growing upward and providing fresh material to be turned into sand.  Kill the reef and the supply of sand and coral rubble will dwindle and storms will no longer have material to keep pace with sea level rise.

Releasing the assets

Releasing the assets of Libya.  Give me a break.  You froze them with a stroke of the pen (or was it with the push of a button).  Now you are having trouble releasing them!!!    You europeans (small e) have been very comfortable holding huge amounts of Libyian oil money for the Colonel.  Propped up your economy, didn't it.  Now if you release the money, it will be a run on your bank.  Don't have the money, do you.  And what about Switzerland - the land of chocolate and coco clocks.  When they hold money stolen from the people of a country by corrupt leaders they just sit on it.  Just look at the time it took for the people of the Philippines to get any of the money back that Markos stole.  I bet Qaddafi has lots of money squirreled away in Switzerland.  I bet Libya won't see any of it any time soon.